Unitary WB trivial to accomplish with Canon DSLR's?

Started Sep 26, 2012 | Discussions thread
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l_d_allan
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Unitary WB trivial to accomplish with Canon DSLR's?
Sep 26, 2012

Here is info on "unitary white balance", also with .cr2 / .nef files from which to set custom white balance for a variety of Canon and Nikon DSLRS:
http://www.guillermoluijk.com/tutorial/uniwb/index_en.htm

The "point" of unitary white balance is to have the jpeg-engine based histogram and "blinkies" behave more like the source was the RAW capture. Done correctly, it facilitates what might be considered as ETTR-Max.

The tutorial also references a Very Simple Procedure to set Canon unitary WB from dark frame (all pixels RGB 0-0-0 from picture of lens cap) or complete over-exposed frame (all 255-255-255, such as 10 seconds pointed up at sky wide open).

Then use that capture (dark frame or white frame) from which to set the Custom White Balance.

Quick check seems to work, at least approximately on my 5dm2 and a friend's 40d. In LiveView and preview of the capture, the image looks Very Green, which is intended / expected. The "blinkies" don't show up for about a stop more open than if "normal" WB used, so the ETTR from the blinkies and/or histogram is that much more to the right.

More info:

A more elaborate technique is to copy the appropriate .cr2 from the website to your CF/SD card, and then use that as the base from which to set Custom White Balance. For the 5dm2, it was a light magenta (which I suspect would be pretty close for most cameras).

I first heard about "unitary WB" from a Nikon user who read about it in a Thom Hogan book. However, their procedure was rather more elaborate, and seemed to involve a custom curve for a "bank". I haven't heard back whether the "capture from a dark frame" would work with Nikon (or other DSLR's)

Note: the intent of this is to make the histogram and "blinkies" be more accurate for RAW captures, rather than the overly-conservative histogram based on the DSLR's jpeg engine. It does not make the senor have better dynamic range or more headroom, or in any way modify the sensor's tone curve.

Feedback appreciated if my understanding of "unitary WB" is incomplete or incorrect.

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